Due to the advancing state of the art in the projection or lithographic printing field, it has become highly desirable to be able to provide image geometries of less than 2 microns and very high device packing densities. In order to most advantageously obtain same, it has become highly desirable that projection imaging wavelengths in the deep ultra-violet (UV) region of below about 300 nm be employed. It is therefore desirable that suitable deep UV resist compositions be available for use with imaging wavelengths in the deep UV region.
Recently U.S. Pat. No. 4,339,522 to R. Balamson et al., issued July 13, 1982 and assigned to International Business Machines Corporation, disclosed such a deep UV resist composition which comprises phenolic-aldehyde resins sensitized with Meldrum's acid diazo or a homologue thereof as a dissolution rate inhibitor for the matrix resin in the unexposed imaging layer. In the exposed regions the inhibition agent undergoes a radiation induced structural transformation which alters its efficiency as a dissolution rate inhibitor for the matrix resin. Thus, the exposed regions are rendered more soluble than the unexposed regions and the difference in solubility rates is utilized to generate the positive lithographic patterns.
However, such sensitizers such as Meldrum's acid diazo and homologues thereof suffer from a lack of thermal stability and undue volatility. As a result there is often a substantial loss of such sensitizing agents during wafer prebake. As a result the sensitizing agent is not completely retained in the photoresist layer and lower prebake temperatures have had to be employed. Another undesirable result has been the fact that the wall profiles of the resist images are somewhat undercut.
The loss of sensitizer that occurs during prebake also results in process variability and inhibit reproducible wafer performance. Also, the UV dosage required to achieve good image quality and useful processing is undesirably high.
Therefore, a need exists for deep UV photosensitive solubilization inhibitors for use in deep UV photoresist compositions which inhibitors possess improved thermal stability, lower volatility and have improved retention in the photoresist composition during prebake operations. Moreover, it is also highly desirable that such inhibitors be able to endure higher prebake temperatures without loss of retention in the photoresist compositions.
Additionally, it is most desirable that such solubilization inhibition agents be available which provide deep UV photoresist compositions having higher lithographic photosensitivity and allowing for usage of lower UV dosages in processing. Another desirable feature would be such solubilization inhibitors that allow for shorter clearing or developing times yet with higher sensitivity. Especially desirable would be the availability of such solubilization inhibitors producing deep UV resist compositions providing good resolution of 0.75 micron lines or smaller.